Spectroscopic Investigations of Hydrogen Bonding Interactions in the Gas Phase. VIII. Microwave Rotational Spectrum of the Heterodimer H-C$\equiv$C -C$\equiv$N$\cdots$HF

The hydrogen bonded dimer formed between cyanoacetylene and hydrogen fluoride has been identified through its infrared and microwave spectra. Two microwave techniques, continuous wave and pulsed-nozzle Fourier transform spectroscopy, have been combined to identify unambiguously the vibrational ground state transitions and to assign vibrational satellites. In making the assignments, much use has been made of computer simulation of spectra, which is described in an Appendix. Analysis of the microwave spectra led to the following spectroscopic constants and molecular parameters.~~~ Finally, the variation of$\Delta\overline{\nu}$ as a function of $r_0(N\cdots F)$ has been examined fora series of dimers RCN $\cdots$ HF.